"Didn’t I tell you to stop leaving your clothes in my fucking room?"
>Dash turns away from her desk to look at you.
>In hindsight, you must make for a pretty hilarious picture, standing in the door to your sister’s room and angrily waving around a black G-string.
>At least you’d think so, judging from the girl’s face.
"It’s not funny!"
>That makes her let out a hearty chuckle.
>"It kinda is." 
>Stretching out the elastic between your fingers, you let it snap back to launch the thong into Rainbow’s face.
>She’s crying with laughter.
>"It’s a prank," she manages to wheeze, her underwear hanging from her mug, "Lighten up!"
>You turn to leave.
>"Wait!"
>Dash peels off the panties to inspect them.
>"Did you nut in it again? It’s all sticky and"—she takes a sniff—"yep, you definitely fapped with this."
"Yeah well, consider yourself pranked, bitch."
>"Did you think of me?"
"Fuck you."
>"Come on, tell me," your sister whines, jumping up to come over and playfully press her body against yours. "You thought about this thing wrapped around my pussy, right?"
>Pulling at the waistband of her sweatpants, she gives you a peek down her crotch.
>It doesn’t look like she’s wearing anything beneath right now.
>"Want me to put it on again, now that it’s full of your cum?"
"Fuck off," you push the girl away, fleeing out of her room to the sound of rough laughter.
 
>This fucking girl.
>It’s been a few weeks since this prank war of yours started, and you have to fight tooth and nail not to end up losing.
>She sent you a picture of her naked breasts at some point—she said it was an accident but you’re not even sure anymore—to which you replied with a full-on dick pic.
>A short video of her fingering herself was answered by you cumming on a printout of her face and leaving it on her desk.
>Now she proceeds to put all kinds of clothes in your room—socks, skirts, and skimpy thongs now, apparently—and you make it a point to return them drenched with ropes of cum every single time.
>Rainbow doesn’t seem to mind too much.
>You need to find a way to get off the back foot sooner rather than later.
 
 
>Sure enough, you find another of Dash’s panties tucked under your pillow the next day. 
>It’s late afternoon by the time you come across the thing, about an hour or so before your parents are supposed to come home from work.
>Just enough time to retaliate.
>You take a moment to study the piece of clothing.
>It’s a cute design today, a white thong with a tiny black ribbon at the front and a bit of black lace framing the fabric.
>You wouldn’t really pick it from a pile if you had to guess what your sister liked to wear, but then again, you didn’t take her for the type to film herself jilling off either.
>Her cute little tuft of manicured pubic hair was a nice surprise, too.
>If the video is anything to go by, Rainbow is pretty conscious of presenting herself in a sexy manner.
>Maybe she just did it for your viewing pleasure.
"Shit."
>You realize you’ve been stroking yourself for a while, already oozing precum into your sister’s latest prank.
>Can’t give in right now.
>You have something different in mind this time.
>Fishing around your drawer for a bit, you pull out the box of condoms you bought a few months ago and roll one of the rubbers down your length.
>With Dash’s video playing on your phone again, you continue jerking off.
>You cum quickly, your mind flooded with the image of your sister’s pussy and the soft scent coming from her thong.
 
>You don’t bother knocking this time.
>"Hey," Rainbow whirls around as you stalk towards her. "I could have been naked!"
"So?"
>You can hear the note of feigned shock in her voice.
>"What if I’d been," she leans in for a stage whisper, "masturbating."
"Nothing I haven’t seen before."
>You flick the panties into the far corner of the room, watching the girl’s façade break into a sly grin.
>"Didn’t use it this time? Can’t even get it up for your sister anymore?"
>She pinches a bit of her belly.
>"Am I getting fat?"
"You’re fine."
>Out of all the things, it actually makes her blush a bit.
"Here."
>Pulling up her hand, you gingerly place the condom from earlier onto her palm.
>It’s tied off at the end and filled with a nice, heavy load of cum.
>"Huh?"
>Dash blinks at the gift a few times before looking up.
>"It’s still warm."
"Yeah well, I just… you know. Used it."
>This is more embarrassing than you thought.
>Who the fuck gives their sister a rubber filled with spunk?
"Hey, what the fuck–"
>Rainbow cuts you off by digging her nails into the condom’s knot to untie it.
>"That’s kinda hot."
>Before you can react, she has opened the thing up again and squeezed the whole fucking load into her mouth.
"Jesus Christ!"
>Her face turns sour almost instantly, and she whimpers while sucking more semen from the latex.
"C’mon, Dash, spit it out! I get it, you’ve won again. Just spit it out. Here."
>You hold out your hand, only for your sister to vigorously shake her head.
>"Nuh-uh. I got thish," she slurps, tilting her head back to try and swallow.
>It takes her a few seconds—and a wet, audible gulp followed by a sigh of relaxation—to actually succeed.
>"All gone," the girl boasts, opening her mouth wide and sticking out her tongue. "Fucking gross though."
>No matter how you look at it, she’s got you again.
>Also, for some reason, you’re sporting a half-chub even though you came not five minutes ago.
"Nasty bitch."
>"You know you love me. And next time skip the silly condom thing, alright? Just…"
>She lets her tongue loll out of her mouth again, rolling back her eyes and throwing up a double peace sign for added effect.
>For the second time in two days, you leave your sister’s room to the sound of laughter.
>And you also know she’s been at your folder with the animated porn again.
 
 
>It’s already late in the evening by the time you sneak into Rainbow’s room again.
>She’s on her back, lying on her bed, lazily tapping at her tablet’s screen.
>Her shirt has ridden up to just above her navel and a pair of black spats is hugging her waist.
>Noticing you closing the door behind you, she props herself up on her elbows.
>"Mom and Dad are asleep already?"
"I hope."
>With that, you unceremoniously grab your dick and pull it out of your sweatpants, starting to fluff it up.
 >"Ha! Now what?" Dash watches you pump, your erection slowly growing. "I didn’t even have a chance to hide anything in your room again."
"Prank time."
>"Yeah?" you sister scoffs. "What are you gonna do, make me watch you giving yourself a tug? Want me insult you while you do it or what? I didn’t know you rolled that way."
>Still stroking, you walk over and gently rub your dick against her cheek.
>She answers by flicking her tongue and quickly lapping up the first drop of glistening precum at the tip.
"I’m just gonna cum in your panties again."
>"Lame!" Rainbow sing-songs. "I’m starting to think you really just have a giant– Hey!"
>Hooking your hand into the waistband of her spats, you pull them away from her belly.
"While you’re wearing them."
>It takes her a moment to catch up, giving you enough time to climb over her thighs and get on your knees.
>You have one leg on each side, with your dick just above her crotch.
>If you angle yourself right, you can give her a nice load down the front of her shorts.
>Rainbow chuckles.
>"Props to you, not a bad idea," she flicks away your fingers to hold her shorts open herself, leaving you free to play with yourself using both hands. "Small problem though…"
>She starts to pull at the waistband, moving it down her hips.
>The motion is slow, seductive, leaving you enough time to follow the line of black fabric giving way to more and more creamy skin.
>"I’m not wearing any."
>Pushing her shorts to her knees, Rainbow reveals her crotch.
>No sexy lingerie, not even another skimpy G-string.
>Just her straight-up pussy.
>"Hey, you sped up!" her grin widens. "It’s nice to have some real-life wanking material, huh? Take it easy though or the fucking slapping’s gonna wake Mom and Dad."
>You honestly don’t think you could.
>Your eyes are fixed on your sister’s sex.
>Her tuft of fluffy hair.
>Her squishy thighs.
>Your hand is all but flying up and down your shaft.
>"So," Dash opens up her legs, letting her hands wander down, "that means I win again, right?"
"Fuck off."
>She brushes over her lips with her fingers, pulling them apart just a bit to reveal the hot pink flesh beneath.
>Circling her clit with one hand, she slowly reaches out with the other.
>"What do you think Mom would say if she walked in right now? Finding her children jack off on top of each other."
"It’s… just a prank, right?"
>"Right," Rainbow chuckles while grabbing your arm, forcing you to stop pumping so she can close her own fingers around your shaft. "Pranked, bro! Epic! I’m totally gonna make you bust a fat nut all over my snatch."
>She starts stroking.
"Then I’m gonna fondle your tits!"
>Leaning forward, you push up her shirt, tracing your sister’s breasts.
>They’re soft and squishy, with two cute nipples standing at attention.
>"No fair!" your sister begins to fap faster. "My tits are sen–"
>Her words get drowned in a sharp moan when you give them a pinch.
>"Fucker!"
>She slaps your dick against her pussy in response.
>"How ya like that, huh? Gonna cum? Gonna–"
>Once again, you manage to cut her off, this time by pressing your lips onto hers.
>The moment she mushes her tongue against yours is the moment you shoot the first rope of hot cum onto her belly.
>Even through the kiss, Dash manages to redirect the second one onto her pussy.
>"Fuuuck," she groans into your mouth, her eyes fluttering.
>You don’t stop kissing her.
>Not when she squeezes the rest of your load onto herself and not when she starts fingering her pussy through the puddle of your jizz.
>You keep letting her bite your lip and suck your tongue while she brings herself to her own climax, all the while eliciting more moans and mewls by playing with her nipples.
 
 
>"I’m on the pill, idiot," Rainbow notices you staring at her cum-covered pussy.
>You’ve been lying next to her for a while now, enjoying the heat of her body radiating into yours.
>A few globs are slowly drying in the bit of fluff that is her pubic hair, the rest of your jizz is pretty much smeared all over.
>You can’t be sure but you think a bit of it is actually dripping from inside of her.
>"It’s safe."
"Do you think this pranking thing has officially gone too far now?"
>"Are you seriously gonna keep calling it that? I think that ship has sailed a while ago. Giving your sister a creampie–"
"I didn’t creampie you!"
>"You did a little bit! Whatever, we’ve safely passed the boundaries of normal sibling skinship, yes."
"So no more pranks?"
>"I guess not…"
>She sounds a bit gloomy about it.
"Probably for the best. You kept winning the damn things."
>"I dunno," Dash lets her fingers trace over your chest, "I think I gotta give you that last one. That kiss fucked me up pretty good."
>You can’t help but smile.
>"Jerk."
 
>"Anon."
>You’re halfway out the door when Dash’s call makes you turn around.
>"Just because we agreed to stop pranking doesn’t mean we can’t…"
>She makes a ring with her fingers and pumps into it with another.
>"We can still… you know… fool around, right?"
"I don’t think I could hold back anyway, Rainbow. Can’t even remember the last time I fapped without your video."
>"Aw," she smiles, "I guess I could make a few more."
>The last thing you see before closing the door is your sister blowing you a kiss, the very gesture making her cheeks burn brighter than you’ve ever seen.
>Even when she was making you shoot your load between her thighs, she wasn’t this flushed.
>Weird how that works.
>The two of you may have a problem after all.
 
 
>Looking back on it, that was probably the start of the slippery slope.
>Although neither you nor Dash recognized it at the time.
>What you found was too alluring—too tempting—not to be ensnared by.
>With the silly pretense of pranking each other out of the way, you were left with pure, intoxicating lust.
>No safety nets.
>No excuses.
>Just the two of you hiding from your parents, kissing and sucking each other’s saliva like it was heroin.
 
>It’s Friday, late in the afternoon.
>Your dad is watching TV downstairs; you think you heard Mom starting dinner a while ago.
>You’re in your room, trying to distract yourself from how aroused you are.
>A knock comes through the door, followed by your sister sneaking in a second later.
"Jesus, Rainbow, did you have to wear that skirt today?"
>Dash looks down, patting imaginary lint from her clothes.
"I can only picture you fucking yourself with that dildo in it. You know, last week?"
>"Sorry."
>She has the decency to look a little guilty.
>"If you can hold out until tonight we might get away with repeating that. Just got to wait until the coast is clear."
"I can’t," you shake your head, "I’m seriously going to go insane before that."
>"You think this is easy for me?" your sister grunts, pointing at your crotch. "You’re practically walking with your dick bulging out your pants here."
>As if to prove her point, she lifts her skirt to reveal—next to the fact that she pulled her thong down to her thighs—reddened skin already slick with arousal.
"Not helping."
>You pull out your dick and start stroking to relieve some of the pressure, nodding for Dash to lean against the door and block any surprise visits from your parents.
>"What are you doing?" she whispers, licking the tips of her fingers and starting to circle her clit. "You’ll never be able to finish before dinner."
"I don’t care. I’ve gotta do something."
>Your sister bites her lip, thinking.
>You can practically see the miniature devil on her shoulder: a small, naked version of herself whispering into her ear.
>It’s winning.
>"Alright, come with me."
"Where?"
>"Just come! Put that thing away and be quiet."
 
>It’s a few minutes later.
>You and Rainbow are stark naked and locked into the bathroom.
>"Shhh," she breathes, one of her hands pumping your shaft while the other is working on your balls. "Mom’s gonna hear you."
>She’s so close that the tip of your dick is poking her belly, leaving glistening smears of precum on her skin.
>You’re eagerly working on returning the favor, with one of your fingers already inside of her.
"She’ll hear ME? You sound like you’re about to give birth. Jesus, you’re wet."
>You add a second finger. 
>"Fuck…" your sister pants in response, a bit of saliva drooling from the corner of her mouth.
>You discovered that particular weak spot a few days ago.
>It still works, judging by the sloppy sounds coming from her pussy.
>She’s getting less coherent with her handjob, too, which isn’t to say that she’s not absolutely getting your rocks off, still.
>Letting a glob of drool fall down for better lubrication, she increases her pace.
 
>"Why aren’t you cumming? Hurry up, Mom’s gonna wonder where we are. We’re fucking dead if she finds us in here, you know?"
"I’m trying."
>"Try harder," Rainbow spits on your cock again, rubbing the tip against her tummy.
"How the fuck can I try harder?"
>"I dunno, think of something hot."
"My sister is about to cum all over my fingers," you give her a deep poke, making her shudder. "I don’t think I’ve got something hotter in my brain right now."
>Dash giggles, the complement, however weird, hitting its mark.
>"Fine," she whispers, turning around, "I’ll help you out. Guess I owe you one for last night anyway."
>You’re lost for a moment, mildly annoyed that her hand is no longer working your dick.
"What are you doing?"
>"I don’t have the size for a titjob and I really don’t want to figure out how to blow a guy in our bathroom under pressure. But you’re always saying how you like my thighs."
>She shakes her hips to give you another hint, slowly backing her butt up against your erection.
"Fuck, Rainbow!"
>"It’s cool, just keep quiet."
>With a quick motion, Dash grabs you from between her legs, closing her thighs around your erection and beginning to rub them together.
>"It’s fffine…"
"Are you sure?"
>"Just try to cum quick," she squirms "I’m a bit sensitive right now."
 
>You can’t say why exactly—instincts, hormones, the intoxicating cocktail of Dash’s smell trapped in the small room—but you start thrusting.
>Your dick begins slipping in and out of that tight, wet-hot gap between your sister’s thighs and pussy.
>It’s almost too much to bear.
>Rainbow herself is mostly held up by you gripping hold of her hips by now, bent over and arching her back.
>"Fuck! This… this was a bad idea after all," she pants. "Stop, Anon! I can’t! I won’t be able to keep it down."
>You don’t stop.
>You can’t.
>All you can do is keep slamming yourself against her ass, fucking her thighs, the wet slaps of the motion quickly growing louder.
>Covering her mouth with her hand, Rainbow tries to stifle another moan.
>It barely even helps, but you don’t care.
"This is great, Rainbow."
>Dash answers by squeezing her thighs together as hard as she can, bouncing back against your dick whenever you thrust forward.
"You’re the best… best fucking sister I could wish for!"
>"Let me turn around."
>It takes considerable effort but you manage to pace yourself for a moment, letting your cock slip out from between the girl’s drenched thigh gap.
>Before you even can admire the sheen of her juices on your member, Rainbow has already spun around and slipped it back in, pressing her body against yours in a tight hug.
>She takes another second to properly adjust its position, however.
>Where you were simply rubbing yourself against her earlier, she guides your erection home this time, impaling herself on it.
>"Fuck…"
"Fuck!"
>For a moment, all you can do is stand motionless, waiting for your nerves to stop shooting electricity through your spine like hot lightning.
>"Okay… I think you can start moving."
 
>Locking her into another kiss, you slowly start pushing in and out of Rainbow’s pussy.
>To her credit, she tries her best to keep up, but it looks like the sensations that have left you panting and groaning have thoroughly overwhelmed your little sister.
>She’s just drooling into your mouth, entirely on the defense.
"Are you sure?"
>She nods into your chest.
>"You know I’m on the pill. I also don’t think we’ll be able to clean the mess you’ll be making in here otherwise. Just do it inside."
>There is a pause, filled with more wet slaps, before she grins up at you.
>"Paint my womb with your baby batter!"
"Have you been at my folder again?"
>"N-no."
>You thrust harder.
>"M-maybe. I just wanted to get some ideas on how to get you going," Rainbow smiles guiltily, her face flushed with pleasure. "Do you like that kind of talk? Want to flood my fuckbox with your cum?"
>You chuckle, just barely keeping your rhythm.
"I love you."
>"Love you, too."
>Surprisingly, you couldn’t have imagined her saying anything hotter.
 
>"Rainbow! Anon! Dinner’s ready, come down!"
>Your mom’s voice coming through the door lets the two of you freeze up.
>"Shit, we gotta go!"
"No! No, please. I won’t be able to sit straight if we stop now. It’s going to look like I’m smuggling a cucumber. Come on, just let me finish. Please!"
>"Anooon," your sister whines. "I’m about to cum again. I’m the one who won’t be able to sit if you keep fucking me. What am I, your own personal masturbation aid?"
>You go back to pumping into her.
>"Is that what you want? Beating your sister’s cute little pussy into submission and having her leak your cum all over herself during dinner? Forcing her to masturbate under the table just thinking about all that hot jizz bubbling in her womb?"
"Yes."
>"You want to knock me up that bad?"
"Yes."
>"Then cum already!"
>Pressing her lips against yours again, Rainbow finally manages to push you over the edge.
 
>The sensation of spurting rope after rope of sticky spunk into Rainbow’s pussy is almost enough to make you pass out.
>Even though she clamps down hard, you still keep thrusting, fucking more and more of your sperm into her.
>You only stop when you can’t move your hips anymore, feeling your sister’s legs give out at the same time.
>Her weight drops against your chest, and you carefully guide her down onto her butt.
>She has to stem the flow of cum with her hand when you pull out, dopily smiling up at you.
>Her hand is still rubbing her clit, riding the aftershocks of her orgasm.
>"Rainbow? Anon?" your mom is calling again.
"Shit! C’mon, snap out of it!"
>"Huh?"
"We gotta go!"
>Blinking for a few seconds, you can see Dash’s eyes clearing up.
>"Fucking hell!" she shakes her head, snapping to attention. "Help me wipe this off! Move! Panties! Get my panties!"
 
 
>"Are you okay, honey? Did you go for a run?" your mom is patting Rainbow’s forehead over the dinner table. "You look flushed. Are you getting a fever?"
>"I’m fine, Mom."
>"You’re burning up!"
>"It’s fine, really. Just a little…" your sister throws you a glance. "Just a little distracted is all…"